Biological and molecular characterisation of potential biocontrol strains of Trichoderma

The G protein alpha subunit Tga1 of Trichoderma atroviride is involved in chitinase formation and differential production of antifungal metabolites

Trichoderma mycoparasitism includes recognition, attack, overgrowth and lysis of the host fungus accompanied by morphological changes and secretion of hydrolytic enzymes and antibiotics. Studying the underlying signal transduction pathways, the tga1 gene encoding a Galpha subunit of Trichoderma atroviride P1 was analysed. A Deltatga1 mutant showed continuous sporulation and elevated internal steady-state cAMP levels. tga1 gene deletion resulted in a complete loss of mycoparasitic overgrowth and lysis of Rhizoctonia solani, Botrytis cinerea, and Sclerotinia sclerotiorum during direct confrontation, although infection structure formation was unaffected. The reduced mycoparasitic abilities were reflected by strongly decreased chitinase activities and reduced nag1 and ech42 gene transcription. Furthermore, production of 6-pentyl-alpha-pyrone and of metabolites with sesquiterpene structure was reduced in the Deltatga1 mutant. Regardless of these deficiencies, the mutant displayed an enhanced growth inhibition of the host fungi by over-producing other low molecular weight antifungal metabolites, suggesting opposite roles of Tga1 in regulating the biosynthesis of different antifungal substances in T. atroviride.

Biological control of agricultural pests by filamentous fungi

Agricultural use of chemical pesticides has polluted the environment and resulted in resistance among the target organisms. The chemical strategies of pest control are dangerous to both the nontarget organisms in natural habitats and human health. Biological control is an attractive less dangerous possibility for controlling plant pathogens.Some methods of biological control are becoming now commercially available against plant parasitic fungi, nematods and insects. Among filamentous fungi many candidates with biocontrol potential can be found. Fungal biocontrol agents are less effective and reliable than the synthetic pesticides therefore their use in the agricultural practice requires genetic improvement.

Homologous transformation of Trichoderma hamatum with an endochitinase encoding gene, resulting in increased levels of chitinase activity

A 42-kDa endochitinase encoding gene, Tham-ch, was cloned by screening the genomic library of Trichoderma hamatum strain Tam-61 with a PCR-amplified chitinase sequence from the same fungus. Tham-ch with its own regulatory sequences was reintroduced into the host strain. The integration of the transforming construct was stable only in one copy. Homologous integration occurred in nine transformants, while non-homologous integration was detected in one transformant. All but one transformant expressed higher levels of chitinase activity in comparison to the wild-type recipient strain; the maximum level of increase was 5-fold. Duplicating the copy number of the highly conserved approximately 42-kDa endochitinase encoding gene appears to be one potential means by which the biocontrol capability of the Trichoderma species might be improved.

Phylogeny of the genus trichoderma based on sequence analysis of the internal transcribed spacer region 1 of the rDNA cluster

Sequences of the internal transcribed spacer region 1 (ITS1) of the ribosomal DNA were used to determine the phylogenetic relationships of species of Trichoderma sect. Pachybasium. To this end, 85 strains-including all the available ex-type strains-were analyzed. Parsimony analysis demonstrated that the section is nonmonophyletic, distributing the 85 strains among three main groups that were supported by bootstrap values. Group A comprises two clades (A1 and A2), with A1 including T. polysporum, T. piluliferum, and T. minutisporum, while A2 included T. hamatum, T. pubescens, and T. strigosum in addition to species previously included in sect. Trichoderma (i.e., T. viride, T. atroviride, and T. koningii). The ex-type strain of T. fasciculatum formed a separate branch basal to clade A. Clade B contained the sect. Pachybasium members T. harzianum, T. fertile, T. croceum, T. longipile, T. strictipile, T. tomentosum, T. oblongisporum, T. flavofuscum, T. spirale, and the anamorphs of Hypocrea semiorbis and H. cf. gelatinosa. Sequence differences among clades A1, A2, and B were in the same order of magnitude as between each of them and T. longibrachiatum, which was used as an outgroup in these analyses. Sequence differences within clades A1, A2, and B were considerably smaller: in some cases (i.e., T. virens and T. flavofuscum; T. strictipile and H. cf. gelatinosa), the ITS1-sequences were identical, suggesting conspecifity. In other cases (e.g., T. crassum and T. longipile; T. harzianum, T. inhamatum, T. croceum, T. fertile, and H. semiorbis; T. hamatum and T. pubescens; and T. viride, T. atroviride, and T. koningii) differences were in the range of 1-3 nt only, suggesting a very close phylogenetic relationship. The sequence of a previously described aggressive mushroom competitor group of T. harzianum strains (Th2) was strikingly different from that of the ex-type strain of T. harzianum and closely related species and is likely to be a separate species. Copyright 1998 Academic Press.

Systematics and environmental application of the genus Trichoderma

Trichoderma, an anamorphic Hypocreaceae (class Ascomycetes), is common in the environment, especially in soils. Species of this genus have been used in the production of cellulolytic and hemicellulolytic enzymes, biological control of plant disease, biodegradation of chlorophenolic compounds, and soil bioremediation. They are also the cause of disease in commercially produced mushrooms. The species Trichoderma has not been clearly defined yet, despite being a very common fungus with an expanding number of applications. Therefore, we highlight the importance of the use of molecular techninques along with conventional methodologies based on morphological characters in order to achieve a "natural" taxonomic system for this group of fungi, as well as for any other complex group of fungi.

Assignment of a PCR-amplified chitinase sequence cloned from Trichoderma hamatum to resolved chromosomes of potential biocontrol species of Trichoderma

A 1424 bp DNA sequence containing the genetic determinants of the chitinase enzyme was identified in Trichoderma humatum by PCR amplification. High levels of similarity were observed between this sequence, named Th-ch (T. hamatum chitinase), and the 42 kDa chitinase genes known from T. harzianum. Chromosome-sized DNAs of five potential biocontrol species of Trichoderma were separated by pulsed-field gel electrophoresis. The total number of chromosomes was six in all the species, with sizes ranging from 3.7 to 7.7 Mb; estimated genome sizes were between 30.5 and 35.8 Mb. When fractionated chromosomes of the five species were probed with radiolabelled Th-ch, strong hybridization signals developed in all cases, but the physical position of these signals varied among species indicating a polymorphic chromosomal location of the highly conserved 42 kDa chitinase gene within the genus Trichoderma.